The present application is based on Japanese Patent Applications Nos. 2001-091961 and 2001-308256, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to what is called a flip-chip-type light emitting diode (hereunder sometimes abbreviated as xe2x80x9can LEDxe2x80x9d) adapted so that alight emitting element is electrically connected to leads through the rear surface electrode thereof. The present invention also relates to a light shielding/reflecting type device adapted so that light outputted from a light source is reflected by a concave reflecting mirror and that the reflected light is radiated from an optical opening portion provided in a light shielding plate, and to the light source therefore. Incidentally, in the present specification, an LED chip itself is referred to as xe2x80x9ca light emitting elementxe2x80x9d. Further, a light emitter sealed with a resin lens is referred to as a xe2x80x9clight sourcexe2x80x9d. Further, the entire light emitting apparatus including an optical device, such as package resin, on which an LED chip is mounted, or as a lens system, is referred to as xe2x80x9ca light emitting diodexe2x80x9d, xe2x80x9can LEDxe2x80x9d or xe2x80x9ca devicexe2x80x9d.
2. Description of the Related Art
Hitherto, a light emitting diode has been constructed by employing what is called a flip-chip structure adapted so that when a light emitting element, such as a GaN light emitting element, having both of an anode electrode and a cathode electrode provided on one side thereof is mounted on an LED diode, the mounting of the light emitting element thereon is performed through a zener diode with the (transparent) electrode side down (see WO98-34285).
An example of such a conventional light emitting diode is described hereinbelow with reference to FIG. 11. FIG. 11 is a sectional view illustrating the configuration of a part, on which a light emitting element of the conventional light emitting diode is mounted, of the conventional light emitting diode. As illustrated in FIG. 11, in this light emitting diode 51, a reflecting mirror 53c is formed from one 53a of a pair of leads 53a and 53b for supplying electric power to a GaN light emitting element 52. A zener diode 54 is mounted on the bottom surface of this light emitting diode 51 by using silver paste. Two kinds of electrodes 54a and 54b are formed on the top surface of the zener diode 54. Two sorts of electrodes provided on the bottom surface of the light emitting element 52 are connected onto those electrodes 54a and 54b by using gold bumps 55a and 55b. Moreover, the light emitting element 52 is mounted thereon. A wire 56 is bonded to one 54b of the electrodes formed on the top surface of the zener diode 54 and electrically connected to the lead 53b corresponding to the other electrode 54b. Thus, the light emitting element 52 is mounted on the zener diode 54 and emits light by being supplied with electric power by the pair of leads 53a and 53b. 
However, in such a light emitting diode 51, the light emitting element 52 is mounted one 53a of the leads through the zener diode 54. Thus, this conventional light emitting diode has drawbacks in that heat dissipation is poor, that consequently, the temperature of the light emitting element 52 rises to a high level, and luminous efficiency lowers, and device lifetime decreases. Further, even when the reflecting mirror 53c is provided in such a way as to surround the light emitting element 52, as illustrated in FIG. 11, the reflecting mirror 53c is away from the light emitting element 52 owing to the zener diode 54, and that thus, sufficient optical characteristics cannot be obtained.
Further, light emitting diodes include a reflective LED. An example of this reflective LED is described hereinbelow with reference to FIG. 12. FIG. 12 is a sectional view illustrating an example of a reflective LED. As illustrated in FIG. 12, this reflective LED 131 has a light emitting element 132 mounted at an end portion of one 133b of a pair of leads 133a and 133b for supplying electric power thereto. Further, the light emitting element 132 is electrically connected to the other lead 133a through wire bonding using a wire 134. The light emitting element 132, the pair of leads 133a and 133b, and the wire 134 are sealed with transparent epoxy resin 135. A reflecting surface, which has a focal point at the position of the light emitting element 132 and is shaped like a paraboloid of revolution, is formed at a place at which the reflecting surface faces the light emitting element 132. A concave reflecting mirror 136 is formed by evaporating aluminum on the outer reflecting surface thereof.
When light is emitted from the light emitting element 132, the light is upwardly reflected by each part of the reflecting mirror 136 parallel to the central axis of the reflecting surface shaped like a paraboloid of revolution. Then, the reflected light is radiated from the top surface, which is a flat radiating surface 137, of the reflective LED 131 to the outside. Thus, the reflective LED 131 can externally radiate the light, which is emitted from the light emitting element 132, as light obtained by being condensed with high efficiency.
However, the conventional reflective LED 131 has problems in that because the area of the reflecting surface seen from the outside is large, large dark noises are caused (that is, what is called pseudo-lighting occurs) owing to the reflection of external light at each turn-off of the light source, and that consequently, the contrast between the intensity of the light, which is radiated during the light source is turned on, and that of the light reflected when the light source is turned off, is low.
Accordingly, an object of the present invention is to provide a light emitting diode, which sufficiently shows the characteristics of a light emitting element, by forming a flip chip structure without using a zener diode, and to provide a manufacturing method therefor.
Another object of the present invention is to provide a light shielding/reflecting type device, which shows high efficiency in external radiation of light and high contrast between the intensity of light, which is radiated during the light source is turned on, and that of light reflected when the light source is turned off, and to provide a light source therefor.
To achieve the foregoing object, according to the invention, there is provided a light emitting diode(hereunder referred to as a first light emitting diode of the invention) having a flip-chip-type light emitting element. In this diode, a through hole of a through-hole substrate is filled with metal. Further, one of rear surface electrodes of the light emitting element is connected onto the through hole. Moreover, the other of the rear surface electrodes of the light emitting element is connected to a conductive pattern insulated from the through hole of the through-hole substrate.
In the case of the LED of such a configuration, fine and precise conductive patterns of the through hole substrate can be formed. Thus, two rear surface electrodes, the distance between which is very short, of the light emitting element can be adapted so that one of the rear surface electrodes is reliably connected onto the through hole, while the other of the rear surface electrodes is reliably connected onto the conductive pattern insulated from the through hole by maintaining the insulation therebetween. Further, because the through hole is filled with metal, the through hole can serve as a heat sink. Thus, the LED excels in heat radiation. Consequently, luminous efficiency is maintained at a high level. The device lifetime can be increased.
Thus, the LED, which sufficiently exhibits the characteristics of the light emitting element, is provided by forming a flip-chip structure without using a zener diode.
According to another aspect of the invention, there is provided a light emitting diode (hereunder referred to as a second light emitting diode of the invention) having a flip-chip-type light emitting element. This diode comprises an insulating film fixed on the top surface of one of a pair of leads for supplying electric power to the light emitting element. This diode comprises two conductive foils formed on the insulating film in such a way as to be away from each other. In this diode, rear surface electrodes of the light emitting element are respectively connected to the two conductive foils. Further, one of the two conductive foils is electrically connected to the one of leads, and the other of the two conductive foils is electrically connected to the other of the pair of leads.
In the LED of such a configuration, the insulating film is fixed onto one of the leads, so that the rear surface electrodes of the light emitting element are insulated from the one of the leads. Further, the rear surface electrodes of the light emitting element are connected to the two conductive foils formed on the insulating film in such a way as to be away from each other. Furthermore, the two conductive foils are electrically connected to the one of the leads and the other lead, respectively. Thus, the rear surface electrodes of the light emitting element are electrically connected to the one of the leads and the other lead, respectively. In this way, the flip-chip structure is formed. Further, the light emitting element is put on the one of the leads through an extremely thin insulating film and the conductive foil. Thus, this LED extremely excels in heat radiation. Consequently, luminous efficiency is maintained at a high level. The device lifetime can be increased.
Thus, the LED, which sufficiently shows the characteristics of the light emitting element, is provided by forming a flip-chip structure without using a zener diode.
According to another aspect of the invention, there is provided a light emitting diode (hereunder referred to as a third light emitting diode of the invention) having a flip-chip-type light emitting element. This diode comprises an insulating film fixed on a top surface of one of a pair of leads for supplying electric power to the light emitting element, and a conductive foils formed on the insulating film. In this diode, one of rear surface electrodes of the light emitting element is connected to the conductive foil. The other of the rear surface electrodes, and the conductive foil is electrically connected to the other of the pair of leads.
In the LED of such a configuration, one of the rear surface electrodes of the light emitting element is connected to the conductive foil insulated from one of the leads through the insulating film. Further, the conductive foil is electrically connected to the other lead by a wire. In contrast, the other of the rear surface electrodes of the light emitting element is connected directly to the one of the leads by a gold bump. Thus, the rear surface electrodes of the light emitting element are electrically connected to the one of the leads and the other lead, respectively. The flip-chip structure is formed in this manner. Further, a part of the light emitting element is put on the one of the leads through an extremely thin insulating film and conductive foil, while the remaining part of the light emitting element is put directly on the one of the leads. Consequently, this LED extremely excels in heat radiation. Further, luminous efficiency is maintained at a high level. The device lifetime can be increased.
Thus, the LED, which sufficiently exhibits the characteristics of the light emitting element, is provided by forming a flip-chip structure without using a zener diode.
According to an embodiment (hereunder referred to as a fourth light emitting diode of the invention) of the third light emitting diode of the invention, a concave reflecting mirror is formed from the one of leads in the third light emitting diode of the invention. Moreover, the light emitting element is placed on the bottom surface of the reflecting mirror.
Light outputted in a horizontal direction from the light emitting surface of the light emitting element is reflected and irradiated by such a concave reflecting mirror in a direction nearly perpendicular to the light emitting surface thereof. Thus, the efficiency in external radiation from this LED is enhanced. Further, one of the rear surface electrodes of the light emitting element is insulated from one of lead by an insulating film and connected to the conductive foil extended to the edge of the reflecting mirror constituted by the one of the leads. Furthermore, the conductive foil is electrically connected to the other lead by a wire. In contrast, the other of the rear surface electrodes of the light emitting element is connected directly to the one of the leads by a gold bump. Consequently, the rear surface electrodes of the light emitting element are electrically connected to the one of the leads and the other lead, respectively. Thus, the flip-chip structure is formed. Therefore, the light emitting element is mounted on the bottom surface of the reflecting mirror through no zener diodes. Consequently, this LED can sufficiently serve as the reflecting mirror. Thus, sufficient optical characteristics can be obtained.
Further, a part of the light emitting element is put on the one of the leads through an extremely thin insulating film and conductive foil, while the remaining part of the light emitting element is put directly on the one of the leads.
Thus, the LED, which sufficiently shows the luminous efficiency, the device lifetime, and the optical characteristics of the light emitting element, is provided by forming both the flip-chip structure and the reflecting mirror without using a zener diode.
According to an embodiment (hereunder referred to as a fifth light emitting diode of the invention) of one of the first to fourth light emitting diodes of the invention, a part of the through-hole substrate or a part of the pair of leads, and the light emitting element are sealed with a light transmissive material. In the fifth light emitting diode, a surface portion, which is provided at the side of a light emitting surface of the light emitting element, of the light transmissive material is formed as a light radiating surface portion.
A quantity of light radiated from the light emitting element sealed with a light transmissive material in this manner is about twice that of light radiated in the case of the light emitting element, which is not sealed. Thus, the efficiency in external radiation is extremely enhanced. Moreover, because the light emitting element is mounted by forming the flip-chip structure without using a zener diode, this LED extremely excels in heat radiation. Furthermore, high luminous efficiency is maintained, and device lifetime increases.
Thus, the LED, which sufficiently shows the luminous efficiency, the device lifetime, and the external radiation efficiency of the light emitting element, is provided by forming the flip-chip structure and sealing the light emitting element with the light transmissive material without using a zener diode.
According to an embodiment (hereunder referred to as a sixth light emitting diode of the invention) of the fifth light emitting diode of the invention, the light radiating surface portion is a convex lens.
Thus, light emitted from the light emitting element is converged and externally radiated by sealing the light emitting element with the light transmissive material and providing the light radiating surface of the convex lens at the side of the light emitting surface of the light emitting element. Thus, this LED excels in optical characteristics. Moreover, the quantity of light radiated from the light emitting element is increased by sealing the light emitting element with the light transmissive material, to a value, which is almost twice that of light radiated from a light emitting element that is not sealed with such a material. Thus, the efficiency in external radiation is extremely enhanced. Moreover, because the light emitting element is mounted by forming the flip-chip structure without using a zener diode, this LED extremely excels in heat radiation. Furthermore, high luminous efficiency is maintained, and device lifetime increases.
Thus, the LED, which more excels in the luminous efficiency, the device lifetime, the efficiency in external radiation and the light convergence characteristics, is obtained by forming the flip-chip structure without using a zener diode, and by sealing the light emitting element with the light transmissive material and by providing a light radiating surface of the convex lens.
According to another aspect of the invention, there is provided a method (hereunder referred to as a first manufacturing method of the invention) of manufacturing a light emitting diode, which comprises the step of sticking an insulating film, on which a conductive foil is put, to a part of one of a pair of leads for supplying electric power to a light emitting element, the step of stamping the one of leads to thereby form a concave reflecting mirror, at the central portion of which one of ends of the conductive foil of the insulating film is placed, and the step of processing a concave surface of the reflecting mirror in such a way as to be round-cornered, and the step of connecting one of rear surface electrodes of the light emitting element to an end of the conductive foil at the central portion of the concave reflecting mirror, and the step of electrically connecting the other end of the conductive foil to the one of the pairs of the leads.
According to this method of manufacturing the light emitting diode, after sticking an insulating film, on which a conductive foil is put, onto one of a pair of leads, the stamping of the one of leads is performed to thereby form a concave reflecting mirror. Then, an end of each of the film and the foil is placed at the central portion of the reflecting mirror. Moreover, a concave surface of the reflecting mirror is processed in such a way as to be round-cornered. Thus, the light emitting element can be mounted at the central portion of the reflecting mirror. Furthermore, the conductive foil can be reliably prevented by round-cornering the concave surface of the reflecting mirror from being cut off during the stamping. Subsequently, at the central portion of the reflecting mirror, one of the rear surface electrodes of the light emitting element is electrically connected to one end of the conductive foil by a gold bump. Moreover, the other of the rear surface electrodes of the light emitting element is connected directly to one of the leads by a gold bump. Then, the other end of the conductive foil is electrically connected to the other lead by a wire. Thus, the flip-chip structure is formed.
According to this method of manufacturing a light emitting diode, the light emitting element can be mounted thereon by utilizing the flip-chip structure without using a zener diode. Moreover, the conductive foil for electrically connecting one of the rear surface electrodes of the light emitting element to the other lead can be reliably prevented from being cut off during the reflecting mirror is formed. Further, the light emitted from the light emitting surface of the light emitting element in the horizontal direction is reflected in the direction, which is nearly perpendicular to the light emitting surface, so that the efficiency in external radiation from the LED is enhanced.
Thus, the heat radiation from the light emitting element is enhanced by forming the flip-chip structure without using a zener diode and by forming a round-cornered concave reflecting mirror. Consequently, the first manufacturing method of manufacturing LEDs, which excels in the luminous efficiency, the device lifetime, and can obtain sufficient optical characteristics, and provide highly reliable electrical connection, is provided.
According to an embodiment (hereunder referred to as a second manufacturing method of the invention) of the first manufacturing method of the invention, the step of sealing a part of the pair of leads, the reflecting mirror, and the light emitting element with a light transmissive material, and forming a surface, which is provided at a side of a light emitting surface of the light emitting element, of the light transmissive material as a light radiating surface is added to the first manufacturing method.
A quantity of light radiated from the light emitting element sealed with a light transmissive material in this manner is about twice that of light radiated in the case of the light emitting element, which is not sealed. Thus, the efficiency in external radiation is extremely enhanced. Moreover, because the light emitting element is mounted at the central portion of the reflecting mirror by forming the flip-chip structure without using a zener diode, this LED extremely excels in heat radiation. Furthermore, high luminous efficiency is maintained, and device lifetime increases, and the efficiency in external radiation is enhanced.
Thus, this LED manufacturing method, which more excels in the luminous efficiency, the device lifetime, and the efficiency in external radiation of the light emitting element, is provided by forming the flip-chip structure without using a zener diode and by sealing the light emitting element with the light transmissive material to thereby form the light radiating surface.
According to an embodiment (hereunder referred to as a third manufacturing method of the invention) of the second manufacturing method of the invention, the light radiating surface portion is a convex lens.
Thus, light emitted from the light emitting element is converged and externally radiated by sealing the light emitting element with the light transmissive material and providing the light radiating surface of the convex lens at the side of the light emitting surface of the light emitting element. Thus, the third manufacturing method excels in optical characteristics. Moreover, the quantity of light radiated from the light emitting element is increased by sealing the light emitting element with the light transmissive material, to a value that is almost twice that of light radiated from a light emitting element that is not sealed with such a material. Thus, the efficiency in external radiation is extremely enhanced. Moreover, because the light emitting element is mounted at the central portion of the reflecting mirror by forming the flip-chip structure without using a zener diode, the third manufacturing method extremely excels in heat radiation. Furthermore, the high luminous efficiency is maintained, and the device lifetime increases, and the efficiency in external radiation is enhanced.
Thus, the LED, which more excels in the luminous efficiency, the device lifetime, the efficiency in external radiation and the light convergence characteristics, is obtained by forming the flip-chip structure without using a zener diode, and by sealing the light emitting element with the light transmissive material and by providing a light radiating surface of the convex lens.
Still further, to achieve the foregoing object, according to an aspect of the invention, there is provided a light shielding/reflecting type device (hereunder referred to as a first light shielding/reflecting type device of the invention) having a light source portion, which has a light emitting portion, a reflecting mirror opposed to a light radiating side of the light source portion, and a light shielding plate, which has an optical opening portion. This device comprises a substrate portion on which the light source portion is mounted. Further, the side, on which the light source portion is mounted, of the substrate portion is black.
Incidentally, the optical opening portion is an opening portion, through which light can pass, and maybe either a through hole or a hole filled with a light transmissive material.
The light shielding/reflecting type device of such a structure has the substrate portion on which the light source portion is mounted. The side, on which the light source portion is mounted, of the substrate portion is black. Thus, even in the case that external light is incident from the optical opening portion when the light source is turned off, the incident light is reflected by the reflecting mirror to the side, on which the light source portion is mounted, of the substrate portion and absorbed thereinto. Therefore, the incident light does not return to the outside. Consequently, an occurrence of pseudo-lighting is completely prevented. Thus, the contrast between the intensity of light, which is radiated during the light source is turned on, and that of light reflected when the light source is turned off, is increased.
Thus, the light shielding/reflecting type device is high in efficiency in external radiation and large in contrast between the intensity of light, which is radiated during the light source is turned on, and that of light reflected when the light source is turned off.
An embodiment (hereunder referred to as a second light shielding/reflecting type device of the invention) of the first light shielding/reflecting type device of the invention further comprises a spacer for changing a height of the substrate portion. This spacer is black.
Thus, the focal length thereof is increased by providing the spacer therein. Consequently, the light shielding/reflecting type device has light distribution characteristics that provide a high degree of light convergence.
According to another aspect of the invention, there is provided a light shielding/reflecting type device (hereunder referred to as a third light shielding/reflecting type device of the invention) having a light source portion, which has a light emitting part, a reflecting mirror opposed to a light radiating side of the light source portion, and a light shielding plate, which has an optical opening portion. In this device, the light shielding plate is formed like film.
The light emitting part of the light source portion has a certain size. Therefore, strictly speaking, light convergence is performed so that light is focused onto a spot having a certain width in the vicinity of a focal point. Thus, in the case that the light shielding plate is thick, the efficiency in external radiation cannot be increased unless the width of the optical opening portion is increased. However, the light shielding plate is formed like a thin film. Thus, even when the width of the optical opening portion is narrow, high efficiency in external radiation can be obtained. Consequently, the width of the optical opening portion can be narrowed. An amount of external light entering the device can be reduced to a minimum value. Hence, the contrast between the intensity of light, which is radiated during the light source is turned on, and that of light reflected when the light source is turned off can be increased.
According to another aspect of the invention, there is provided a light source (hereunder referred to as a first light source of the invention) having a light emitting element, a light transmissive material, with which the light emitting element is sealed, and a substrate. In this light source, a part, on which the light emitting element is mounted, of the substrate is formed as a heat radiation conductive member. Moreover, the heat radiation conductive member leads to the back surface of the substrate.
Thus, the light emitting element is mounted on the heat radiation conductive member of the substrate. Further, the heat radiation conductive member leads to the back surface of the substrate. Thus, heat outputted from the light emitting element is transferred through this heat radiation conductive member to the back side of the substrate. Consequently, the efficiency in radiation of heat outputted fro the light emitting element is enhanced very much.
According to an embodiment (hereunder referred to as a second light source of the invention) of the first light source of the invention, a convex lens is formed from the light transmissive material in the first light source.
Therefore, light emitted from the light emitting element is caused by this convex lens to impinge upon the interface between the element and the light transmissive material at an angle in such a manner as to be nearly perpendicular thereto. Thus, when the second light source is used as the light source for the light shielding/reflecting type device, the light convergence is enhanced. Moreover, the efficiency in external radiation is increased to a high level.
According to an embodiment (hereunder referred to as a third light source of the invention) of the first or second light source of the invention, the substrate is shaped so that the four corners of the substrate are cut off.
Thus, because the four corners of the substrate are cut off, light reflected by the reflecting mirror is not blocked off by the four corners of the substrate when this light source is used in the light shielding/reflecting type device. Consequently, the light reflected by the reflecting mirror is externally radiated and effectively utilized.
According to an embodiment (hereunder referred to as a fourth light source of the invention) of the second light source of the invention, (a width of the substratexe2x88x92a diameter of the convex lens)xe2x89xa61 mm.
As compared with what is called a lead type light source, what is called a substrate type light source is advantageous in that because the lead is not protruded from the side surfaces thereof, the width of the substrate type light source can be narrowed by an amount for that. Thus, the size of the entire light source can be reduced by keeping an amount, by which the width of the substrate partly protruding from the convex lens is larger than the diameter of the convex lens, within 1 mm.
According to another aspect of the invention, there is provided a light shielding/reflecting type device (hereunder referred to as a fourth light shielding/reflecting type device of the invention) using the fourth light source of the invention.
In the case of the fourth light source of the invention, the size of the entire light source is reduced by keeping the amount, by which the width of the substrate partly protruding from the convex lens is larger than the diameter of the convex lens, within 1 mm. The use of such a light source in the light shielding/reflecting type device enables space-saving, change of the light source in such a way as to be close to a point light source, and more enhancement of efficiency in external radiation.
According to another aspect of the invention, there is provided a light shielding/reflecting type device (hereunder referred to as a fifth light shielding/reflecting type device of the invention) that comprises a substrate portion on which a light source portion is mounted. In this device, a part, on which the light source portion is mounted, is a heat radiation conductive member. Further, the heat radiation conductive member leads to the back surface of the substrate portion.
Thus, the light source portion is mounted on the heat radiation conductive member of the substrate portion. The heat radiation conductive member leads to the back surface of the substrate portion. Consequently, heat outputted from the light source portion is transmitted to the rear side of the substrate portion through the heat radiation conductive member. Thus, the efficiency in radiation of heat outputted from the light source portion is enhanced very much.
To sum up, according to the present invention, there is provided a light emitting diode comprising: a substrate having a heat radiation conductive member therein; and a light emitting element mounted on said substrate, at least a part of said light emitting element being directly brought into contact and electrically connected with said heat radiation conductive member.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.